1. Technical Field
The present invention relates to a nonvolatile memory device, and more particularly to a programmable voltage generator for the nonvolatile memory device.
2. Description of Related Art
In integrated memory devices, a high voltage source or generator (i.e. programmable voltage generator) is required for word line pumping or to supply a programming voltage in the nonvolatile memory devices. The output level of the high voltage source is programmable, and in general the output level can be set by fuses and stepping up with programming shot to shorten the programming time. Thus, it is possible that the output voltage of the high voltage source is higher than the level which can be sustained by the memory device. The memory device, at least, includes row decoder, column decoder, memory cell, and so on. The programmable voltage generator provides a programming voltage greater than required by a load device (such as a memory cell and word line decoder or sustainable voltage in the programmable voltage generator).
However, if the programming voltage provided by the programmable voltage generator is higher than a breakdown voltage of the load device or the device in the programmable voltage generator, the load device or the programmable voltage generator may be failed or useless. Therefore, a limiting circuit is connected in parallel with the programmable voltage generator and the load device to limit the maximum level of the programming voltage provided by the programmable voltage generator.
In a continuous operation, the programmable voltage generator programming voltage can provide the sufficient current to supply the load device at the limited programming voltage, thus programming the load device successfully. Unfortunately, the programming voltage required by the load device is varying along with the semiconductor process variation, and that is, the load devices made of by the different semiconductor processes may have different programming voltages. The integrated circuit designer must design the different limiting circuits for the load devices made of by the different semiconductor processes, and thus it increases the product cost and design time for manufacturing the nonvolatile memory devices.